Arachin 18 - Age for Symbolic Value
Symbolic value of a person vowed to the Temple depends on his or her age, and if A vows to give the value of B, it is the age of B, not A, that matters.
The thirtieth day of an infant is considered as days before, and this infant has no symbolic value yet. Similarly, the fifth year is considered as years before, and so the twentieth, which results in lower symbolic values. Why? The Torah said, " From sixty years of age and higher " to teach that only subsequent years are included. But how can we derive anything from the sixtieth year, when the symbolic value decreases, resulting in a stringency, and apply the rule to the twentieth year, when the value increases, resulting in a leniency? - We learn it from an extra word "years" in the phrase "from five years to twenty years" where "from five years to twenty" would have been enough.
At sixty the symbolic value of a man drops by 70%, but that of a woman drops significantly less. Why? Chizkiyah quoted a proverb, "An old man in a house is a calamity, but an old woman in a house is a treasure."
Art: Diego Rodriguez de Silva y Velazquez - Old Woman Frying Eggs